It’s probably not even a good idea to try and defend against the bubble by switching up your stock allocation. After all the whole reason passive investing works is that active investment rarely beats the market and if you’ve just been in SPY the whole time it’s unlike you have any edge to gain by switching to an active strategy every time fear creeps up
All of that is only true if the market is sufficiently diversified and not manipulated for profit extraction.
Right now it's not clear that is true.